Unintentionally-soured wort?!

I thought this would be pretty commonplace but can't find out much otherwise online...

Brewed a batch of around OG 1.6, used a relatively old smackpack of Wyeast 1762, made a starter, it still wasn't showing activity by the time I brewed... kept the wort in the pot (securely covered) for at least 36 hours, pitched the starter and everything smelled good for at least the first day. Now it has an unequivocally-staunchy smell. What to do? I'm guessing that it's not harmful to drink, but just stinky?

What you could be smelling could just be normal fermentation. Besides 'staunchy' what else does it smell like? What does it look like too? In the future, if your starter isn't showing activity by the time your brew session is done, just go ahead and pitch it into the wort rather than keeping the sweet wort around for a day and a half.

BTW, an OG of 1.6? There has to be a typo somewhere.